Evaluation of the Surface Topography of Corroded Old Cast Iron Pipes

Paper No. 92
Doctor Zohreh Soltani Asadi1, Professor Robert E. Melchers1 – 1The University Of Newcastle, Callaghan, Australia

Abstract

Pitting corrosion is among the main reasons of the failure of cast iron water main distribution world- wide. Estimating the growth and the progression of pits along the surfaces of pipes would assist in predicting the remaining service life of the pipes. To aim this, in this study, topographies of the surfaces of old cast iron pipes (up to 129 years) are investigated by computing the contour maps of the surfaces. The analysis of the digital contour maps from real pipes supports previous observations that pitting corrosion is not a continuous process. It appears that a sequence of events occurs, in stages, which changes the topographies of the surfaces. Soon after first exposure, micro pits are generated, and these grow in both size and depth. A number of pits may grow faster and eventually form larger pits, termed broad or macro pits. A new population of pits then tends to initiate on the inside surfaces of broad pits, which results in the pits having a bench like shape. Since other pits nucleate and commence to grow after a time, or stop growing, it was seen that after a long exposure period there were still a significant number of isolated pits on the surfaces.

 



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